Conventionally, there is known a power conversion device that includes an inverter circuit having a plurality of semiconductor switching elements, and a switching control section for controlling driving of the semiconductor switching elements. Such power conversion devices are widely used for, for example, home electrical appliances, industrial equipment, and the like for which the rotation rate or torque of a motor needs to be controlled.
In order to operate the motor efficiently, it is desirable to perform so-called vector control for controlling voltage and current in accordance with the speed and the rotor position of the motor. For performing the vector control, a predetermined sensor is provided to detect the speed and the rotor position of the motor, but this leads to cost increase of the power conversion device.
Therefore, so-called sensorless vector control has been widely applied which performs motor control without detecting the speed and the rotor position of the motor by a sensor. In the sensorless vector control, the speed and the rotor position of the motor are estimated from voltage applied to the motor and current flowing in the motor. In a general power conversion device, a voltage command is used as the voltage applied to the motor in this case.
In the power conversion device, generally, a flyback diode is connected in antiparallel with each semiconductor switching element. Due to ON voltage drop when current flows in the semiconductor switching element or the flyback diode, the actual voltage applied to the motor has error from the voltage command. As a result, distortion occurs on output current or torque. In addition, since the actual voltage applied to the motor has error from the voltage command as described above, instability or the like in the sensorless vector control arises.
Considering the above, for example, as in Patent Document 1 below, a method of correcting the voltage command taking into consideration ON voltage drop when current flows in the semiconductor switching element or the flyback diode, is proposed.